1. Field of the Invention
The present invention relates to an antilock brake control system in a vehicle, including wheel speed detecting means for detecting a wheel speed, a vehicle speed presuming means for presuming a vehicle speed based on the wheel speed detected by the wheel speed detecting means, a slip rate calculating means for calculating a slip rate based on the wheel speeds detected by the wheel speed detecting means and the presumed vehicle speed determined in the vehicle speed presuming means, a target slip rate determining means for determining a target slip rate based on the presumed vehicle speed determined in the vehicle speed presuming means, a deviation calculating means for calculating a deviation between the target slip rate determined in the target slip rate determining means and the slip rate calculated in the slip rate calculating means, and a PID calculating means for carrying out a PID calculation based on the deviation determined in the deviation calculating means, the result of a calculation in the PID calculating means being used to control the operation of a braking fluid pressure regulating means.
2. Description of the Related Art
Such a control system is conventionally known, for example, from Japanese Patent Application Laid-open Nos. 6-144195 and 7-117653.
However, the above known control system is arranged to linearly control the braking pressure based on the result of the calculation in the PID calculating means and hence, an expensive linear solenoid or the like is required as a braking pressure controlling actuator, and a common inexpensive on-off operated solenoid valve cannot be used as such a braking pressure controlling actuator. Therefore, in order to provide a reduction in cost, it is desired that an antilock brake control can be performed in a simple structure using an inexpensive on-off operated solenoid valve. Moreover, even if the arrangement is such that the antilock brake control is performed in a simple structure with the on-off valve, it is necessary to prevent the occurrence of an excessive control or a control delay.